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View Full Version : To the moon then to Mars bogus??



anybody
2009-Mar-31, 04:03 AM
Nasa is planing to go to the moon build a base there, then build a ship to go from the moon to Mars.

Would it not be better to build the Mars ship in Earth orbit, using ISS as a base ??

01101001
2009-Mar-31, 04:12 AM
Nasa is planing to go to the moon build a base there, then build a ship to go from the moon to Mars.

Where did you learn that? That's no plan, even dream, I'm familiar with.

What I am familiar with is relatively near-term plans to return to the Moon. That would test out a lot of ideas and technology for manned missions to Mars, so it is a part of long-range Mars plans. But, I don't think anyone's planning on going from the Moon to Mars.

Read Lunar Exploration Analysis Group 2007 Annual Meeting (http://www.lpi.usra.edu/meetings/leag2007/presentations/) for some outlines of NASA and other nations' space agencies plans for manned missions to the Moon and Mars.

slang
2009-Mar-31, 07:41 AM
Nasa is planing to go to the moon build a base there, then build a ship to go from the moon to Mars.

I suspect you've seen headlines like "From the Moon to Mars", in connection to Bush's Vision for Space Exploration (http://en.wikipedia.org/wiki/Vision_for_space_exploration). I don't think you should take it very literally.


Would it not be better to build the Mars ship in Earth orbit, using ISS as a base ??

Yes, on orbit, probably no on ISS. It is not in an orbit that maximizes launch capability, and for a Mars mission that is probably needed.

tracer
2009-Mar-31, 02:16 PM
I wonder, though ... a moonbase offers the opportunity to have a great big sealed-off pressurized area where people can work in shirtsleeves and gravity. A space station would have neither the size to provide a large indoor work area, nor enough gravity to walk around and use tools without having to put on the mountain-climbing gear needed to work in space (try turning a wrench in zero g without getting spun in the opposite direction!).

centsworth_II
2009-Mar-31, 02:32 PM
I wonder, though ... a moonbase offers the opportunity to have a great big sealed-off pressurized area where people can work in shirtsleeves and gravity.
Think of the surplus equipment and energy required to lift the material for a Mars rocket out of Earth's gravity well, land it on the Moon and then lift it again off the Moon. Not only would you need to lift all the material needed for the Mars trip off the earth, but you would need to lift all the material needed for a Moon landing and Moon liftoff off the Earth as well.

I imagine that the material and fuel requirement for an Earth-Moon-Mars trip could be double that of an Earth-Mars trip.

raptorthang
2009-Mar-31, 02:52 PM
Think of the surplus equipment and energy required to lift the material for a Mars rocket out of Earth's gravity well, land it on the Moon and then lift it again off the Moon. Not only would you need to lift all the material needed for the Mars trip off the earth, but you would need to lift all the material needed for a Moon landing and Moon liftoff off the Earth as well.

I imagine that the material and fuel requirement for an Earth-Moon-Mars trip could be double that of an Earth-Mars trip.

Not only that. The quality standards would need to be incredible. Think of the attention to details of sending up a satelite, probe, etc. The material for a Mars destination woud then need to be reloladed on the Moon and then sent to Mars. Who would do this and with what equipment? folks have this idea of a 'moon base' out of an SF novel...it's not for any foreseeable future. Basically it will be a stripped down ISS. Think how much effort and the time and resources that have been made just to build the space station in LEO.

antoniseb
2009-Mar-31, 03:02 PM
If you're going to build a base on some other body to create a Mars rocket, may I suggest Apophis? Use as much of that thing as you can, and take it with you.

Buttercup
2009-Mar-31, 04:54 PM
"Moon to Mars" means establishing a lunar base first...then going to Mars (via Earth-based launch) and establishing a base there. :)

anybody
2009-Mar-31, 05:20 PM
I think assembling the Mars ship in from prefabricated sections in earth orbit would be the best approach.

Ara Pacis
2009-Apr-07, 05:18 AM
Moon then Mars is a statement of priorities for space development, not an actual mission plan.

novaderrik
2009-Apr-07, 08:30 PM
Moon then Mars is a statement of priorities for space development, not an actual mission plan.
yup- first we take the short trip to the moon, and apply what we learn towards the 2 year trip Mars and back.
it's not like the first raft ever invented was used to cross the Atlantic ocean. it took a few upgrades and design changes before they had a craft capable of making the trip and a crew with the knowledge to do it.

centsworth_II
2009-Apr-07, 09:14 PM
I think that between Moon and Mars Missions, an asteroid mission would be useful, AND interesting.

byronm
2009-Apr-08, 12:37 AM
I was watching some tv show that talked about a rail launch system from the moon.. what is the escape velocity to get out of the moon and then use gravity assists to travel through the solar system?

Siguy
2009-Apr-08, 01:33 AM
The escape velocity of the moon is 2.38 km/s. Since the moon has no atmosphere, a mass driver definitely makes sense. I suppose it could be used to launch rockets toward Earth, which would then use Earth's gravity to further increase their speed. Assuming a constant 3g acceleration, it would have to be 96.5 km long, and require 175 megawatts, (assuming it's launching 5000 kg payloads) so it will be a long time before we have anything like that on the moon.

Jerry
2009-Apr-09, 05:40 PM
I think that between Moon and Mars Missions, an asteroid mission would be useful, AND interesting.

This is what the Planetary Society has proposed, actually skipping a Lunar landing and developing the deep space travel technology necessary to travel first to an asteriod, then to Mars. I would go one step further, and send a manned flight to Phoebe rather than Mars.

centsworth_II
2009-Apr-09, 06:44 PM
This is what the Planetary Society has proposed...I would go one step further, and send a manned flight to Phoebe rather than Mars.
I think we are too politically invested in going to the Moon first to change that. Phoebe is a great idea. The robotic exploration of Mars would be greatly sped up and enhanced with real time human control that could be provided from Mars orbit. Think of all the rovers that could be carried on such a mission in place of a human Mars landing craft! Not having to design a safe-for-humans landing system for Mars right away would also greatly simplify and speed up our first trip there.

Siguy
2009-Apr-09, 08:39 PM
This is what the Planetary Society has proposed, actually skipping a Lunar landing and developing the deep space travel technology necessary to travel first to an asteriod, then to Mars. I would go one step further, and send a manned flight to Phoebe rather than Mars.
You mean Phobos, not Pheobe, right? Biiiig difference.

novaderrik
2009-Apr-09, 11:36 PM
I think we are too politically invested in going to the Moon first to change that. Phoebe is a great idea. The robotic exploration of Mars would be greatly sped up and enhanced with real time human control that could be provided from Mars orbit. Think of all the rovers that could be carried on such a mission in place of a human Mars landing craft! Not having to design a safe-for-humans landing system for Mars right away would also greatly simplify and speed up our first trip there.
yeah, but how would you like to be on a ship that is circling another planet and not be allowed to land on it and go explore for yourself?

JonClarke
2009-Apr-09, 11:56 PM
yeah, but how would you like to be on a ship that is circling another planet and not be allowed to land on it and go explore for yourself?

I can only see this happening if planetary protection requirements render a Mars landing out of the question.

Jon

centsworth_II
2009-Apr-10, 12:19 PM
I can only see this happening if planetary protection requirements render a Mars landing out of the question.

Jon
Astronauts on the first flights to the Moon did not land. Why would would the buildup to landing on Mars be any different?

Suppose we have the technology to send humans into Mars orbit 20 years before we perfect the technology to land them on Mars. Should we wait the extra 20 years before going to Mars or send an orbiting mission in the meantime?

JonClarke
2009-Apr-13, 10:07 PM
Astronauts on the first flights to the Moon did not land. Why would would the buildup to landing on Mars be any different?

Suppose we have the technology to send humans into Mars orbit 20 years before we perfect the technology to land them on Mars. Should we wait the extra 20 years before going to Mars or send an orbiting mission in the meantime?

I suspect that a lot would depend on the mission architecture. If you were aiming at a short stay mission (whether sprint, low thrust, flyby-lander, opposition trajectories) then a non landing precursor mission may well be an attractive precursor.

If you were going to do a conjunction class mission then it is less so. First of all there are a number of higher risks associated with a conjunction class mission that does not land compared to one that does. You are exposing the crew to an extra 18 months in microgavity and a moderately high radiation environment - not as high as interplanetary space but still higher than on the surface.

Secondly, while there is certainly a lot that could be done from LMO - teloperation of vehicles UAVs, sample return vehicles, and laboratories, plus visits to Phobos and Deimos, These would require a lot of development themselves, cdollectively perhaps as much as the actual lander and support systems.

However, once a Aves V or requivalent is operation we could certainly do a flyby or short stay orbital mission almost immediately. Whether it would be worth doing, from the perspective of a rational exploration program, what it might impact on other exploration programs, such the Moon or NEAs, and whether it would usefully contribute to the eventual landing, is something for debate.

Jon

novaderrik
2009-Apr-13, 10:50 PM
going to Mars and not landing makes about as much sense as driving non stop from New York to San Francisco and taking a picture of the Golden Gate without at least driving across the thing before turning around for a non stop drive home.
the moon is only a couple of days away- so not landing the first couple of times makes some sense. but Mars is a half a year away. the technology could be tested with an unmanned landing before the manned mission is launched. the advantage to this would be that the first mission to land could have supplies for the crew when they actually show up- like components for some sort of a prefab living quarters or something packed in where the people would be.

slang
2009-Apr-15, 06:57 AM
You mean Phobos, not Pheobe, right? Biiiig difference.

Not to derail the thread, but I'm pretty sure he means Phoebe, IIRC Jerry made some remarks that it should be investigated for gravity/density reasons. Would be nice, I think we'll find it's an old comet though. Mars first, then crazy trips :)

TampaDude
2009-Apr-15, 12:01 PM
Whatever we do, we need to get some HD images of the Apollo 11 landing site, so we can shut up the "moon landing was faked" CT nuts once and for all.

Grey
2009-Apr-15, 01:38 PM
Whatever we do, we need to get some HD images of the Apollo 11 landing site, so we can shut up the "moon landing was faked" CT nuts once and for all.They'll just say the pictures of the landing site were faked. Or that NASA had unmanned craft secretly land all that stuff there two years ago, just to make it look like we had landed there back in the 60's. :rolleyes:

centsworth_II
2009-Apr-15, 03:44 PM
Not to derail the thread, but I'm pretty sure he means Phoebe....I think we'll find it's an old comet though.
If Phoebe is a comet and not just another asteroid then we absolutely, positively have to go there!

rommel543
2009-Apr-15, 06:35 PM
Long before we go to Mars I think that we need to get private industry into space exploration and mining.

If a private corporation had the resources and the go-nads, the collection of near earth asteroids would provide a HUGE amount of mining potential. Develop a craft that is intended to stay in space, and used to go out and mine asteroids. The craft would then return to earth where the resources would then be transported back down to the planet. Once that corporation completes a few trips and proves it can be completed then additional crafts can be created. Along with the crafts, orbital docks/repair stations could be created where the resources are unloaded and any required repairs can be completed. Also can be used to build the craft in space instead of attempting to bring it up from the planet surface.

NASA can then purchase/lease one of the crafts for interplanetary missions instead of developing their own. Less government spending and increase in technology.

Grey
2009-Apr-15, 07:47 PM
Long before we go to Mars I think that we need to get private industry into space exploration and mining.

If a private corporation had the resources and the go-nads, the collection of near earth asteroids would provide a HUGE amount of mining potential.The problem is that it's not cost effective with our current technology, or anything we can forsee in the relatively near future. Right now, even if there were solid gold bars sitting in nice neat piles on the moon ready for us to take them, it still would cost more to go get them than they would be worth.

JonClarke
2009-Apr-15, 10:31 PM
The problem is that it's not cost effective with our current technology, or anything we can forsee in the relatively near future. Right now, even if there were solid gold bars sitting in nice neat piles on the moon ready for us to take them, it still would cost more to go get them than they would be worth.

Sad but true. That is why space mining will initially be subsistence mining, extracting materials to minimise the amount that needs to be brought from Earth, rather than for export.

ravens_cry
2009-Apr-18, 04:58 PM
A moon base could provide lunar regolith as radiation shielding, as well as oxygen for the crew, and, if water ice is discovered, hydrogen for fuel cells, and possibly aluminum for a rocket, if the ship used chemical fuels. If the base grows it's own food, it could provide that to the orbiting ship. All this at a less cost, in itself, then dragging it all out off Earths gravity well. Of course, you have the cost of setting up the base in the first place.

Siguy
2009-Apr-18, 05:01 PM
An asteroid would be much more useful for raw materials, maybe not ice, but metal, and you don't have to drag anything out of any gravity well.

centsworth_II
2009-Apr-18, 07:03 PM
A moon base could provide lunar regolith as radiation shielding...
In the distant future perhaps, but not for the first, second, third... manned Mars mission.

ravens_cry
2009-Apr-18, 10:42 PM
In the distant future perhaps, but not for the first, second, third... manned Mars mission.

Depends. which do we go for first? manned mission for Mars, or a base on the moon? The things I posited are pretty low end materials. It wouldn't take a very advanced base to provide them. ANY long term base is going to need oxygen ,and it is plentiful in in lunar rocks. Smelting aluminum is another thing entirely, it was once so tough here it was a precious metal, is it doable? I hope so, because you have a rocket fuelled entirely by in situ materials, as well as a good construction material. With no atmosphere, I would imagine a reusable rocket would be much easier to build. Bull dozing lunar regolith onto the base itself is going to be needed for it's own radiation shielding.
Plants have been grown in lunar soil, I imagine food plants could be too, without the need for heavy hydroponics.
Just to clarify, the Mars vehicle would remain in orbit, supplies brought up by the aforementioned reusable lander, fueled by in situ materials.

JonClarke
2009-Apr-19, 12:04 AM
An asteroid would be much more useful for raw materials, maybe not ice, but metal, and you don't have to drag anything out of any gravity well.

Actually the Moon is a much better source than asteroids for titanium, aluminium, and probably copper as well.

And it is much easier to mine and process ore in a gravity well than outside it.

cjameshuff
2009-Apr-19, 12:25 AM
Actually the Moon is a much better source than asteroids for titanium, aluminium, and probably copper as well.

And possibly not a bad one for iron...probably lots of little unoxidized bits that can be magnetically separated from regolith.



And it is much easier to mine and process ore in a gravity well than outside it.

It's nice to be able to put stuff in a pile and have it stay there. Bins that work are nice too. Asteroid mining is going to have to take a very different approach to some things...bags and centrifugal settling of contents, for example. The lunar environment would prove useful in working out approaches to building machinery and processing material that work well in low-gravity vacuum, while being a much more familiar environment in some ways. It's also close, allowing monitoring and remote operation of equipment from Earth and regular resupply, and if necessary, evacuation.

The moon's gravity well isn't that big, it takes just a couple km/s to escape. For trips elsewhere in the system, the nearby gravity well of Earth is useful in doing flyby maneuvers.

Noclevername
2009-Apr-19, 01:08 AM
Astronauts on the first flights to the Moon did not land. Why would would the buildup to landing on Mars be any different?

Because it takes two days to reach the Moon and two years to reach Mars. And it's a lot more expensive.

JonClarke
2009-Apr-19, 09:13 AM
And possibly not a bad one for iron...probably lots of little unoxidized bits that can be magnetically separated from regolith.

True, all nicely comminuted already, plus a high Ni content as well.

centsworth_II
2009-Apr-19, 09:01 PM
Depends. which do we go for first? manned mission for Mars, or a base on the moon? The things I posited are pretty low end materials. It wouldn't take a very advanced base to provide them....
If you plan to build a self sustaining moon base first, before going to Mars, then a manned Mars mission is a lot farther off than one based on all Earth resources. Your way may make sense, it just puts a manned Mars mission that much further in the future.

centsworth_II
2009-Apr-19, 09:10 PM
Because it takes two days to reach the Moon and two years to reach Mars. And it's a lot more expensive.
I assume the logic behind the two-stage approach is, 'let's get the problems worked out of the transit phase first before taking on the landing phase'. Does this logic no longer apply?

Both Mars mission transit and landing are much more complicated than transit to and landing on the Moon. Taking on all the problems on the first try may be taking on too much. It may be cheaper to try it all in one shot, but is it smart?

cjameshuff
2009-Apr-19, 10:09 PM
I assume the logic behind the two-stage approach is, 'let's get the problems worked out of the transit phase first before taking on the landing phase'. Does this logic no longer apply?

The logic applies, but the relative difficulty of the two is now very different. The trip to Mars is far more difficult and risky than the trip to the moon, while the landing on Mars is in some ways simpler, due to sufficient atmosphere for aerobraking and parachutes to be of use. Also, at the time of the Apollo missions, we had far less experience with landing on either the moon or Mars...we hadn't even sent the Viking landers yet. In 1968, when Apollo 8 made the first moon flyby, we'd just lost 2 out of 7 Surveyor landers over the previous 2 years. We'll have accumulated even more experience by the time we get to the point of sending a manned mission to Mars.

And in any case, the likely approach would be for the the manned mission to follow an unmanned landing of a base/return craft/fuel plant. If that successfully lands, there's little reason for the manned craft not to land, if it fails, they probably won't even launch.

Jerry
2009-Apr-19, 10:10 PM
You mean Phobos, not Pheobe, right? Biiiig difference.

Ya, but I'd rather go to Pheobe

ravens_cry
2009-Apr-19, 10:35 PM
If you plan to build a self sustaining moon base first, before going to Mars, then a manned Mars mission is a lot farther off than one based on all Earth resources. Your way may make sense, it just puts a manned Mars mission that much further in the future.
Not exactly self sustaining, just one that makes use of in situ resources. Think of it this way. You could have a large craft for both lunar and Mars trips. For most trips, the stripped down version just goes between Earth and Lunar Orbit. Then when needed for such, it is fueled up, supplies are brought aboard, and extra shielding is added in lunar orbit, and then sent to Mars.

GeorgeLeRoyTirebiter
2009-Apr-20, 04:08 AM
[...]while the landing on Mars is in some ways simpler, due to sufficient atmosphere for aerobraking and parachutes to be of use.

I remembered reading somewhere that it wasn't quite so simple, and a quick search turned up this UT article from 2007: http://www.universetoday.com/2007/07/17/the-mars-landing-approach-getting-large-payloads-to-the-surface-of-the-red-planet/
wherein Rob Manning of JPL explains that we don't really know how to get a large craft safely to the surface of Mars.

Parachutes and aerobraking work for the small landers we've been sending to Mars, but there's not enough atmosphere to make either of those practical for a manned lander.

JonClarke
2009-Apr-20, 09:50 AM
I remembered reading somewhere that it wasn't quite so simple, and a quick search turned up this UT article from 2007: http://www.universetoday.com/2007/07/17/the-mars-landing-approach-getting-large-payloads-to-the-surface-of-the-red-planet/
wherein Rob Manning of JPL explains that we don't really know how to get a large craft safely to the surface of Mars.

Parachutes and aerobraking work for the small landers we've been sending to Mars, but there's not enough atmosphere to make either of those practical for a manned lander.

That story would be a surprise to the many people who have done studies of manned mission landings over the past 40 years and not encountered any fundamental problems (which is not the same thing as saying it is not a challenge.

It's always good to read the fine print of the original study, rather than a journalist's interpretation. When you do, a number of things stand out:

1) Manning and others used a number of assumptions which, while fine for the pruposes of the study, are assumptions and should not be taken as indicating that manned landings are impossible. In particular these included: very high entry masses (up to 100 tonnes, which no study in ther past 40 years has ever postulated) and low lifgt entry vehicles.

2) Manning and others do not state that it is impossible only that further work needs to be done, especially in the field of large diameter, high Mach number (2.5-3.0) parachutes, supersonic descent engine ignition, and high lift entry vehicles.

3) Much of this technology already exists, at least in prototype, it just needs to be validated under martian EDL contions. For example, a wide range of high lift entry vehicles exist, called lifting bodies and biconics.

Jon

Larry Jacks
2009-Apr-20, 01:13 PM
I remember watching a series about sending humans to Mars a year or so ago. It showed researchers from a number of countries discussing different facets of the mission. The Russian researchers had pretty well ruled out using parachutes. IIRC, their reasoning was that a powered descent was less risky than using parachutes followed by a partial powered descent.

Noclevername
2009-Apr-20, 09:36 PM
I assume the logic behind the two-stage approach is, 'let's get the problems worked out of the transit phase first before taking on the landing phase'. Does this logic no longer apply?

Well, we are talking about politicians here.


Both Mars mission transit and landing are much more complicated than transit to and landing on the Moon. Taking on all the problems on the first try may be taking on too much. It may be cheaper to try it all in one shot, but is it smart?

See previous answer.:)

OK, all snarking aside, realistically it all depends on a lot of decesions by a lot of people, most of whom know or care little about science or engineering. So we could end up with almost anything. One thing we can count on, though, is stung pride; if it looks like China is getting close to the Moon, the U.S. will scramble to get back there first.

JonClarke
2009-Apr-20, 10:58 PM
I remember watching a series about sending humans to Mars a year or so ago. It showed researchers from a number of countries discussing different facets of the mission. The Russian researchers had pretty well ruled out using parachutes. IIRC, their reasoning was that a powered descent was less risky than using parachutes followed by a partial powered descent.

What program was that? I'f like to see it. It is good have the Russian studies get an airing. RPO Energia did a number of studies using a parachute free arropaapproach. This greatly influenced the International Space University Mars missions study (well worth the read). They also looked extensively at high lift entry vehicles and horizontal landing, both very good ideas (IMHO) that were also takjen up by the ISU study.


The trick is to get down from 4 km/s on entry (assuming you are in orbit) down to zero. This can be divided into phases, a hypersonic to high supersonic phase from entry down to Mach 3, a supersonic phase down to about Mach 1, and a subsonic landing phase.

The first phase is by normal atmospheric braking. However terminal velocity on Mars, no matter how to design you spacecraft, is probably going to be supersonic.

No matter how you decide to descend, you need rockets for the final landing. Airbags aren't going to cut it.

So the question is how to slow down from Mach 3 down to zero without lithobraking in the process. One option is to use parachutes to slow from about Mach 3 down to Mach 0.5 and use rockets just for the final part of the landing. the other is to use rockets for the whole thing. As always there is a tradeoff between different viable options. Parachutes require less mass, but introduce complexity with a whole extra steps (probably several steps because it probably won't be one parachute that does it all, but a series of them). Rocket only is simpler, but more massive, you use a lot of propellant to slow down. This costs payload mass and payload volume.

Either way we are going to need some development work. If we use parachutes we need research into taking ones about the size of those we curently use to return the shuttle SRBs up to Mach 3 (the MSL parachute deploys at Mach 2.7, I understand, but it is less than half the diameter needed). If rockets, then we need to develop rockets that can fire through (or past) a supersonic shock front. Current rockets operate in the shadow of such shock fronts.

There is nothing to suggest either of these is impossible. My own preference is for parachutes because it increases surface mass and volume. But whether this is the safest will need work.

Jon

GeorgeLeRoyTirebiter
2009-Apr-21, 12:09 AM
I never said (nor deliberately implied) that landing on Mars is impossible, just difficult. I was countering cjameshuff's claim that landing on Mars is simpler than landing on the Moon because of the presence of an atmosphere on Mars. Developing a new deeply-throttleable engine for a lunar lander is much simpler than developing a lifting-body Mars lander with supersonic parachutes or braking rockets.

cjameshuff
2009-Apr-21, 12:23 AM
I never said (nor deliberately implied) that landing on Mars is impossible, just difficult. I was countering cjameshuff's claim that landing on Mars is simpler than landing on the Moon because of the presence of an atmosphere on Mars. Developing a new deeply-throttleable engine for a lunar lander is much simpler than developing a lifting-body Mars lander with supersonic parachutes or braking rockets.

Simpler was not the right word to use...it is in some ways easier, because you don't need to rely purely on rocket power to bring yourself to a soft landing on the ground, but the atmosphere certainly makes it more complex.

JonClarke
2009-Apr-21, 08:33 AM
As an example of how the atmsophere makes things easier for landing on Mars is the fact that you can shed between 85 and 95% of your entry velocity of 4 km/s from orbit using atmospheric breaking alone. As a result EDL systems mass only 30-40% of the descent mass. For comparison, >65% of the mass of the Apollo LM was the EDL system for a much lower velocity change of only 1.6 km/s

Larry Jacks
2009-Apr-21, 12:50 PM
Originally Posted by Larry Jacks
I remember watching a series about sending humans to Mars a year or so ago. It showed researchers from a number of countries discussing different facets of the mission. The Russian researchers had pretty well ruled out using parachutes. IIRC, their reasoning was that a powered descent was less risky than using parachutes followed by a partial powered descent.

What program was that? I'f like to see it.

I'm not positive but I think it was "Mars Rising" on the Science Channel. Here's a link to a promo video (http://science.discovery.com/videos/mars-rising-clips-ep-1-the-challenges.html). I checked their website and it appears the program isn't out on DVD yet. It was a pretty good series. Each hour long episode took one portion of the mission and examined the challenges and the research currently underway.

The first phase is by normal atmospheric braking. However terminal velocity on Mars, no matter how to design you spacecraft, is probably going to be supersonic.

No matter how you decide to descend, you need rockets for the final landing. Airbags aren't going to cut it.

So the question is how to slow down from Mach 3 down to zero without lithobraking in the process. One option is to use parachutes to slow from about Mach 3 down to Mach 0.5 and use rockets just for the final part of the landing. the other is to use rockets for the whole thing. As always there is a tradeoff between different viable options. Parachutes require less mass, but introduce complexity with a whole extra steps (probably several steps because it probably won't be one parachute that does it all, but a series of them). Rocket only is simpler, but more massive, you use a lot of propellant to slow down. This costs payload mass and payload volume.

Either way we are going to need some development work. If we use parachutes we need research into taking ones about the size of those we curently use to return the shuttle SRBs up to Mach 3 (the MSL parachute deploys at Mach 2.7, I understand, but it is less than half the diameter needed). If rockets, then we need to develop rockets that can fire through (or past) a supersonic shock front. Current rockets operate in the shadow of such shock fronts.

There is nothing to suggest either of these is impossible. My own preference is for parachutes because it increases surface mass and volume. But whether this is the safest will need work.

IIRC, the Mars rovers used aerobraking to slow down to low supersonic speeds before deploying a parachute, then used airbags for the final landing (with some help from retrorockets). The Mars Phoenix used a parachute until close to the surface followed by rockets for the landing.

From what I remember of the program, the Russians believed parachutes represented an unnecessary risk for a manned mission. As I understood their argument, you can simplify the reentry and landing profile by using aerobraking to slow down to low supersonic speeds and rocket power for the rest of the way to the surface. Eliminating the parachutes gets rid of a failure mode - if the chutes don't open, you either have to have enough rocket power to land without them (and if so, why bother with the chutes in the first place?), you lose the crew, or you might have to attempt a risky abort.

JonClarke
2009-Apr-21, 10:57 PM
I'm not positive but I think it was "Mars Rising" on the Science Channel. Here's a link to a promo video (http://science.discovery.com/videos/mars-rising-clips-ep-1-the-challenges.html). I checked their website and it appears the program isn't out on DVD yet. It was a pretty good series. Each hour long episode took one portion of the mission and examined the challenges and the research currently underway.


IIRC, the Mars rovers used aerobraking to slow down to low supersonic speeds before deploying a parachute, then used airbags for the final landing (with some help from retrorockets). The Mars Phoenix used a parachute until close to the surface followed by rockets for the landing.

My understanding is that parachutes for historic US landings are designed to open at Mach 2 to 2.5


From what I remember of the program, the Russians believed parachutes represented an unnecessary risk for a manned mission. As I understood their argument, you can simplify the reentry and landing profile by using aerobraking to slow down to low supersonic speeds and rocket power for the rest of the way to the surface. Eliminating the parachutes gets rid of a failure mode - if the chutes don't open, you either have to have enough rocket power to land without them (and if so, why bother with the chutes in the first place?), you lose the crew, or you might have to attempt a risky abort.

I think that is a good summary. Of course the price you pay is the deed to develop technology to fire through shock fronts. You might be able to mount the engines high in a shoulder position and fire into the stagnant zone behind the shock front. But both the Energia designs and the one in the ISU mounted the engines low so had to fire directly though the shock front.

The other issue is the amount of propellant needed to slow down from about 600 m/s rather than 200 m/s. This can make for a big reduction in surface payload. As I recall the Energia studies were for two person landers that also carried the ascent spacecraft. These massed close on 70 tonnes on entry and could support only a couple of weeks of surface operations. These used hypergolics as propellant. The ISU landers carried four people, but were accompanied by several cargo landers to support 18 month surface operations. Propellants massed some 20% of the total, add another 10% for the TPS and it is quite comparable with a parachute system. I can't find what propellant was used though, but it may have been methane-LOX.

So if you can solve the supersonic firing issue and storable cryogenics it might be better approach. If you can't then you use parachutes as an intermediate step.

Jon

GeorgeLeRoyTirebiter
2009-Apr-22, 03:23 AM
I'm not positive but I think it was "Mars Rising" on the Science Channel. Here's a link to a promo video (http://science.discovery.com/videos/mars-rising-clips-ep-1-the-challenges.html). I checked their website and it appears the program isn't out on DVD yet. It was a pretty good series. Each hour long episode took one portion of the mission and examined the challenges and the research currently underway.

Not surprisingly, someone put it on YouTube.

Mars Rising episode 5: Six Minutes of Terror (http://www.youtube.com/view_play_list?p=B3410A2B82650CB7&playnext=1&playnext_from=PL)

JonClarke
2009-Apr-22, 12:21 PM
Thanks for the link. It's not bad, in fact, for a TV documentary, it is quite good, despite being a bit breathless in places. There were only a few errors, and a few more misrepresentations.

Hopefully the rest of the series is on line somewhere.

bunker9603
2009-Apr-23, 03:40 PM
Hopefully the rest of the series is on line somewhere.

They are all available from the link GeorgeLeRoyTirebiter posted :)

JonClarke
2009-Apr-23, 10:07 PM
Yeah, so I discovered!

RGClark
2009-May-02, 01:16 PM
Not surprisingly, someone put it on YouTube.

Mars Rising episode 5: Six Minutes of Terror (http://www.youtube.com/view_play_list?p=B3410A2B82650CB7&playnext=1&playnext_from=PL)

Just saw this article on another idea for landing large, multi-ton payloads on Mars:

Doughnut balloon-chute spaceships to reach Mars, Neptune.
Rocket braking is so retro <cough>
By Lewis Page
Posted in Space, 17th April 2009 11:26 GMT
http://www.theregister.co.uk/2009/04/17/doughnut_ballutes_go_to_mars/
(BTW, the writing on this site is hilarious.)

This is different than the inflatable aeroshell, heat shield, discussed in that video.
This would instead be an inflatable toroidal balloon, a ballute, that trails behind the vehicle to slow it down but also would provide aerodynamic lift.


Bob Clark

danscope
2009-May-04, 04:28 AM
What about the "HEAT"?::doh:

01101001
2009-May-04, 05:12 AM
What about the "HEAT"?::doh:

Besides what the article (http://www.theregister.co.uk/2009/04/17/doughnut_ballutes_go_to_mars/) provided?


In order to avoid getting awfully hot, the plan would be to fly through the thin upper reaches of the atmosphere at hypersonic speeds, with most of the braking provided by the inflatable ballute rather than the ship itself.

What sort of heat do you imagine? Mars Odyssey and Mars Reconnaissance Orbiter did aerobraking without melting their parts.